LAN and/or WiFi bandwidth Monitoring and authentication

I've recently entered the network supplying market and I've gotten to
the point where I need to be able to authenticate users / pc's so not
to only give them access to the internet, but also manage the amount
of data being downloaded per user.

I've met up with our wonderful friend Mr.IP Cop and some of it's add ons
buddies which does exactly this, but to a VERY limited extent.

TCAR it is called, helps but it bombs out my internet connection once you
move further than two WiFi devices away from my IP Cop Gateway/proxy/DHCP/TCAR
server.

I know freeRadius (actualy I know the word RADIUS) exists and I know it
might help with what I'm trying to accomplish. And well, that's about all I know.
O, and I know cacti can help with WiFi devices...but only for monitoring I
think, not for managing. E-Box is also a grate package (has user creation,
SAMBA file sharing, DHCP, Proxy , Firewall etc.) but no bandwidth
management.

ISP Config can manage bandwidth per domain/user and there is quite the
support for it on this forum (I am a big fan of this package as well b.t.w.),
so I know SOME body has to know what I'm talking about.

If some one knows "How To Setup an AAA Server using open source"
or knows of a package install for just that, please post it or feel free to
contact me or just reply to this thread.

Yeah, I don't think this to be the simplest of topics. It's like they say:

"Nothing worth doing is is ever easy"

It will just be strange if nothing like this exists because EVERY software
system I've come across on the Internet that handle's this type of
requirements, is either built on Fedora or it's on a Debian distro.
And they really are ludicrously expensive. I won't go into that topic now...

Anycase, I checked out that link but that is aimed more at capping and
managing your hosting clients. ISP Config does that just perfectly

So I'll wait patiently - maybe some body some where has some beans to spill

How does the "big dog's" (AKA - ISP Companies) do it?
I'm just thinking out loud.